I suppose this could be called a consumable item. When I searched for information on the MAF sensor (MB calls it the Air Mass Meter, or AMM) I got the impression most people needed to replace it at around 70K.

My search also found information that warned people of cheaply rebuilt sensors that use a VW sensing element, which has different electronic characteristics that are bad for the engine management system. The replacement unit should only be a Bosch. The price of these is near $250.

Some vendors sell just the insert. If you can find just the insert you stand to save some money.

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95 E320 Cabriolet, 169K